One present day method to rotatably control the directivity of a directional antenna is to provide the mast upon which the antenna is attached with a rotator connected mechanically thereto and the rotation of the rotator is controlled to mechanically rotatably control the antenna, thereby setting the directivity.
This method, however, inevitably includes mechanically movable portions of very slow speed for rotatably controlling and setting the directivity.
This makes it impossible to presently achieve the follow-up function to automatically set the directivity of antenna in the optimum direction when the received radio waves rapidly change, or when the antenna receiving system moves incessantly. The above problem is worsened by multipath interference, in which the demodulated signal quality is severely deteriorated.
An antenna for a frequency band below the VHF band is very large-sized from a viewpoint of practical use, and is difficult to install and creates many problems in maintenance and safety.
For this reason, an antenna system is required which directionally rotates at high speed, and enables the directivity to be set automatically and electrically in the optimum direction, and has a good follow-up performance. The antenna system also is required to be composed of an antenna of small size and of high gain.